1. Field of the Invention
The present invention relates to an improved liquid crystalline resin, and more particularly, to a liquid crystalline resin and a molded product thereof improved in color, hydrolytic resistance, and heat resistance, with reduced evolution of acetic acid during residence in the molding machine.
2. Description of the Related Art
Plastics having new functions have recently been developed one after another to meet demands for sophisticated technologies. One of them is an optically anisotropic liquid crystalline polymer characterized by molecular chains arranged parallel to one another. It is attracting attention because of its good flowability and mechanical properties. In addition, it finds increasing use for small molded products in the electric and electronic industries and the field of office machines and equipment on account of its high rigidity.
Known examples of liquid crystalline polymers are given below.
a copolymer of p-hydroxybenzoic acid and polyethylene terephthalate. (Japanese Patent Publication No. 18016/1981) PA1 a copolymer of p-hydroxybenzoic acid, polyethylene terephthalate, aromatic diol (such as 4,4'-dihydroxybiphenyl), and aromatic dicarboxylic acid, with improved flowability and heat resistance. (Japanese Patent Laid-open No. 30523/1988) PA1 a copolymer of p-hydroxybenzoic acid, 4,4'-dihydroxybiphenyl, t-butylhydroquinone, and terephthalic acid. (Japanese Patent Laid-open No. 164719/1987) PA1 a copolymer of p-hydroxybenzoic acid, 4,4'-dihydroxybiphenyl, isophthalic acid, and terephthalic acid. (Japanese Patent Publication No. 24407/1982 and Japanese Patent Laid-open No. 25046/1985) PA1 a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. (Japanese Patent Laid-open No. 77691/1979) PA1 incorporation with a heat stabilizer (such as organophosphorus compound and hindered phenol) at the time of polymerization, for improvement in long-term heat resistance. (Japanese Patent Publication No. 51524/1990). PA1 incorporation of phosphorous acid or phosphinic acid or a metal salt thereof into liquid crystalline polyester and/or liquid crystalline polyester amide. (Japanese Patent Laid-open No. 53605/1996) PA1 incorporation with an organophosphorus compound while the reaction product is still in molten state. (Japanese Patent Laid-open No. 32880/1994) PA1 incorporation of an organophosphorus compound into a resin composed of non-liquid crystalline polyester and liquid crystalline polyester. PA1 the heat stabilizer disclosed in Japanese Patent Publication No. 51524/1990 is not totally effective against thermal degradation (leading to discoloration) during residence in the molding machine. PA1 the liquid crystalline polymer disclosed in Japanese Patent Laid-open No. 30523/1988 is subject to slight discoloration due to residues of acetylating agent added in excess (1.1 times in mol for the terminal hydroxyl group) at the time of polymerization. PA1 the procedure disclosed in Japanese Patent Laid-open No. 53605/1996 is not applicable to products which need a good color because an acetylating agent is added in excess at the time of polymerization as in the case just mentioned above. PA1 the procedure disclosed in Japanese Patent Laid-open No. 32880/1994 is not effective against discoloration because of incorporation with an organophosphorus compound as well as an acetylating agent in excess amount. PA1 the procedure disclosed in Japanese Patent Laid-open No. 17974/1995 is not effective against discoloration because of incorporation with an organophosphorus compound. PA1 aromatic dicarboxylic acids, such as 3,3'-diphenyldicarboxylic acid and 2,2'-diphenyldicarboxylic acid. PA1 aliphatic dicarboxylic acid, such as adipic acid, azelaic acid, sebacic acid, and dodecanedionic acid. PA1 alicyclic dicarboxylic acid, such as hexahydroterephthalic acid. PA1 aromatic diols, such as chlorohydroquinone, methylhydroquinone, 4,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfide, and 4,4'-dihydroxybenzophenone. PA1 aliphatic and alicyclic diols, such as 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol. PA1 aromatic hydroxycarboxylic acids, such as m-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid. PA1 p-aminophenol and p-aminobenzoic acid, and derivatives thereof. PA1 electrical and electronic parts for gear, casing, sensor, LEP lamp, connector, socket, resistor, relay case, switch, coil bobbin, capacitor, variable capacitor case, optical pick-up, oscillator, terminal board, transformer, plug, printed wiring board, tuner, speaker, microphone, headphone, small motor, magnetic head base, power module, housing, semiconductor, liquid crystal, FDD carriage, FDD chassis, motor brush holder, parabolic antenna, computers, etc. PA1 parts for VTR, television set, iron, hair dryer, rice cooker, microwave oven, audio laser disc, compact disc, lighting apparatus, refrigerator, air conditioner, typewriter, word processor, home electric appliance, office machine, office computer, telephone set, facsimile, etc. PA1 mechanical parts for washing jig, oilless bearing, stern shaft bearing, underwater shaft, motor, lighter, typewriter, etc. PA1 precision parts for microscope, binocular, camera, watch, etc. PA1 automotive parts for alternator terminal, alternator connector, IC regulator, potentiometer base (for light dimmer), exhaust gas valve and other valves, fuel pipe, exhaust pipe, intake pipe, air intake manifold, fuel pump, engine coolant joint, carburetor main body, carburetor spacer, exhaust gas sensor, coolant sensor, oil temperature sensor, brake pad wear sensor, throttle position sensor, crankshaft position sensor, air flow meter, air conditioner thermostat base, heating warm air flow control valve, radiator motor brush holder, water pump impeller, turbine vane, wiper motor, distributor, starter switch, starter relay, transmission wire harness, window washer nozzle, air conditioner panel switch board, fuel solenoid valve coil, fuse connector, horn terminal, electric insulating board, step motor rotor, lamp socket, lamp reflector, lamp housing, brake piston, solenoid bobbin, engine oil filter, ignition system case, etc.
The above-mentioned liquid crystalline polymers, however, are liable to discoloration during polymerization and molding and also to thermal degradation that aggravates mechanical properties because of their relatively high melting point compared with ordinary polyesters such as polyethylene terephthalate and polybutylene terephthalate. Several countermeasures have been devised as follows.
The above-mentioned prior art technologies have been found unsatisfactory as follows.